1. Field of the Invention
The present invention relates to a brushless-motor driver for driving a brushless-motor employing a pulse-width-modulation (hereinbelow called xe2x80x9cPWMxe2x80x9d) driving technique, for use in various fields of, for example, information equipment such as information-processing devices.
2. Description of the Prior Art
Conventionally, there has been used a brushless-motor driver (or motor driving apparatus) of a synchronous rectification type employing a PWM driving method, as disclosed in the Japanese Patent Unexamined Laid-open Publication No. 5-211780. In this conventional driving apparatus which includes drive transistors and paired drive transistors for switchably providing driving current to motor-driving coils, when the drive transistors are in a PWM switching-off state, the paired drive transistors are turned on to flow current therethrough instead of providing a regeneration current to flow through diodes connected in parallel to the respective paired drive transistors when PWM switching is OFF, thereby reducing power dissipation.
FIG. 5 shows a configuration of the conventional brushless-motor driver employing the synchronous rectification PWM driving method. Referring to FIG. 5, reference numeral 320 denotes a commutation controller circuit; 340 denotes a synchronous rectification controller circuit; 360 denotes a 2-phase non-overlapping clock circuit; and numerals 4 to 6 and 7 to 9 respectively denote upper drive transistors and lower drive transistors. In addition, numerals 10 to 12 and 13 to 15 respectively denote flywheel diodes; 303 to 304 individually denote comparators; VM denotes a power supply terminal; 305 denotes an RC discharge circuit; 302 denotes a flip-flop; 301 denotes an inverter; 1 to 3 individually denote motor-driving coils; and 80 denotes a current-sensing resistor.
Hereinbelow, a description will be made regarding a PWM driving operation of the conventional brushless-motor driver shown in FIG. 5.
During an energized phase, one node (for example, node A) is driven high by one of the upper drive transistors 4 to 6 (for example, by the drive transistor 6). One node (for example, node B) is driven low by one of the lower drive transistors 7 to 9 (for example, by the drive transistor 8), and the other node (for example, node C) is left floating with both the upper drive transistor 4 and lower drive transistor 7 being OFF. Driving coils are then switched in a commutation sequence that maintains the current in one driving coil during switching.
During a PWM mode, the current is sensed across the current-sensing resistor 80, and is compared to a reference voltage VREF by the comparator 303, which determines the maximum current that can be developed in the driving coils 1, 2, and 3. As the current reaches the reference voltage VREF, the comparator 303 flips its output to reset the flip-flop 302. Thereby, the upper transistors 4 to 6 are switchably controlled through the inverter 301, the 2-phase non-overlapping clock 360, and the commutation control circuit 320 to shut off the upper transistors 4 to 6 across all the output nodes A, B, and C.
Simultaneously, the RC discharge circuit 305 is enabled, i.e., is driven to be operable by opening a switch 306, and the RC discharge circuit 305 creates a time delay during which the upper transistors 4 to 6 are maintained OFF. When the voltage on a capacitor of the RC discharge circuit 305 falls below the reference voltage, the output of the comparator 304 reverses and toggles the flip-flop 302, thereby turning the upper transistor which corresponds to the phase being driven, back on again. As a result, the current ramps up, that is, the current diagonally rises. Then, a series of this operation cycle is repeated.
Description is continued using an AB phase by way of an example. First, during the ON time, the current ramps up via the driving coils 2 and 3 between the nodes A and B, and flows through the ON-selected upper transistor 6.
Subsequently, when the upper transistor 6 is shut off in a PWM chop cycle operation, the flywheel diode 15 in parallel with the lower transistor 9 must forward bias to maintain the current in the driving coils 2 and 3, maintaining the electric potential of the node A high. The lower transistor 8 must remain ON to maintain the node B low.
In addition, when the PWM chop cycle shuts off the upper transistor 6, the driving coils 2 and 3 turn into a decaying current source, and the energy stored therein must be dissipated. It is provided through a driving current being applied to the lower transistor 9 from a non-rectifying ground return path for the flyback energy in the active driving coil when a drive voltage to the active driving coil is turned off in the PWM mode. Thus, when the upper transistor 6 is shut off, the lower transistor 9 is turned on, and thus the circuit would appear as if the driving coils 2 and 3 were shorted through two resistors, and no diode were provided. The switching operation of the lower transistors 7 to 9 is accomplished with the synchronous-rectification controller circuit 340 in synchronism with signals developed by the commutation control circuit 320, as below described in detail.
FIG. 6 shows only a portion for one phase of the motor driver circuit as a portion of a control circuitry 300 that is to be provided in the control circuitry 300 shown in FIG. 5. However, it should be understood that similar circuitry is provided for the remaining phases. The control circuitry 300 is a logic circuit configured such that an upper-driving-transistor driving circuitry and a lower-driving-transistor driving circuitry are driven according to commutation signals on lines 384 and 383. Other signals to be input to the control circuitry 300 are sent from the flip-flop 302, as shown in FIG. 5.
To assure that both the upper and lower driving transistors are not simultaneously active, the 2-phase clock 360 is provided having two output signals V361 and V362 which carry exclusively out-of-phase clock signals. The 2-phase clock 360 operates to turn on the upper transistor when the paired lower transistor is turned off, and it operates to turn on the lower transistor when the paired upper transistor is turned off. Hereinbelow, the terminology xe2x80x9csynchronous rectification PWMxe2x80x9d refers to performance of the above PWM operation of both the paired upper and lower transistors.
Thus, in the above-described conventional example, the control circuitry 300 enables the switching between synchronous-rectification PWM operation and normal linear operation.
However, in the above-described conventional configuration, the PWM-operation pulse-width (duty), which is proportional to a torque command, decreases in the synchronous rectification PWM operation according to variations in the motor revolution, variations in load, or a deceleration command as a torque command. This creates a problem in that the regeneration current flowing across the driving coils reversely flows to a power supply. The reverse current hereinbelow will be referred to as a negative current.
In addition, problems arise in that with the aforementioned negative current flowing, the power supply voltage is increased according to an impedance on the power supply side, thereby causing breakdown in the motor and the motor driver, or a device set including the motor.
Moreover, in order to control the motor at an arbitrary revolution number, the PWM duty proportional to the torque command needs to be varied in the PWM drive mode, and the motor application voltage needs to be varied proportional to the torque command in the linear drive mode. This arises problems in that the circuitry configuration is complicated, causing an increase in cost and other various adverse effects are caused. Furthermore, a problem arises in that the linear operation requires increased power consumption.
The present invention has been developed to solve these problems inherent to the conventional motor driver. Accordingly, an object of the present invention is to provide a brushless-motor driver that enables implementation of reduction in power consumption, preventing negative current from occurring due to variations in revolution and load of the brushless motor, and enables the implementation of high performance as well as high reliability.
In order to achieve the aforementioned object, a first aspect of the present invention provides a motor driver for driving a brushless motor having a plurality of driving coils, which includes: a pair of an upper drive section and a lower drive section operatively connected to the driving coils for operating the brushless motor in a plurality of operation modes including a synchronous rectification PWM mode and a one-way PWM mode; and a switching controller for controllably switching the PWM modes between the synchronous rectification PWM mode and the one-way PWM mode in a phase-switching timing period.
In this arrangement, the PWM operation mode is switched to perform the one-way PWM operation mode during a deceleration period in operating the brushless motor, and the synchronous rectification PWM mode is performed in a non-deceleration period thereof, to thereby switch a regeneration current flowing path.
Thus, the present invention solves the problem of causing breakdown in a motor, a motor driver, or a device set including the motor caused by increase in power supply voltage according to the power supply impedance increased by the flow of the negative current.
In this first aspect, the upper and lower drive section pair may include paired drive switching units for switchably providing driving current to the driving coils, and when one of the paired drive switching units is in a PWM switching-off state in the non-deceleration period of the motor drive, the other of the paired drive switching units is turned on to flow a regeneration current through said the other drive switching unit via the driving coils, whereas, when one of the paired drive switching units is in a PWM switching-off state in the deceleration period of the motor drive, the other of the paired drive switching units is also turned off to flow the regeneration current through a diode connected in parallel to the other drive switching unit.
Thus, a low-loss operation can be implemented in comparison to the case of a linear operation. Concurrently, the flow of negative current to the power supply can be prevented.
A second aspect of the present invention provides a motor driver for driving a brushless motor which includes a rotor magnet and driving coils disposed to oppose the rotor magnet, where the motor driver includes: upper drive means constituted of a plurality of drive elements which are connected to the driving coils and are provided on one power supply line; and lower drive means constituted of a plurality of drive elements which are connected to the driving coils and are provided on another power supply line.
The motor driver further includes: position detector means for detecting a positional relationship between said rotor magnet and said driving coils; commutation switching means for generating a commutation switching signal to be supplied to the driving coils based on output signals of the position detector means; pulse-width modulator means which receives a torque command signal for controlling a generated torque of the brushless motor and generating an arbitrary frequency signal having a pulse width corresponding to the torque command signal; and PWM control means for controlling on/off operation of the upper drive means and lower drive means based on output signals of said commutation switching means and an output signal of the pulse-width modulator means.
In this arrangement, the PWM control means enables a synchronous rectification PWM operation to drive both the upper drive means and the lower drive means to perform a PWM operation, and said PWM control means does not perform the synchronous rectification PWM operation in a deceleration period in which a brake-wise current flows through said driving coils.
According to the above second aspect, the motor-revolution control can be implemented with low power consumption, and can be easily implemented by using a PWM signal proportional to the torque command signal. In addition, the synchronous rectification PWM operation is not performed in the timing, allowing a brake current to flow to the driving coils because of variations in the motor revolution, load, and the like. Accordingly, occurrence of negative current can be prevented; and various problems occurring due to the flow of negative current can be prevented.
Conceivable driving methods to be implemented with timing allowing brake-wise current to flow to driving coils include, for example, a method for causing only one of the upper and lower drive means; a method in which neither the upper drive means nor lower drive means is driven to perform PWM switching, but regeneration current is used to implement a short brake mode; and a method of turning the upper and lower drive means off (state where the motor output is of high impedance). Employing one of these methods enables low power consumption, low costs, high performance, and other advantages to be obtained.
In this second aspect, the motor driver may further include deceleration detector means for detecting a deceleration period in the torque command signal and supplying a detection result to the PWM control means.
In addition, the PWM control means may include a regeneration current control means for switching between on/off operations of the upper drive means and the lower drive means so that regeneration current in the driving coils which occurs during motor rotation due to the on/off operation of one of the upper drive means and said lower drive means does not reversely flow back to the power supply line.
This is effective in that the motor is controlled according to a PWM signal proportional to the torque command signal, and switching is performed for current paths through which regenerated current occurring due to the PWM operation flows, thereby preventing occurrence of negative current.
Conceivable timings for performing switching of the regenerated-current paths include, for example, a timing with which deceleration in a torque command is detected; a timing corresponding to a torque command signal, such as a torque command or the result of a comparison with a signal level proportional to the torque command and deceleration in the torque command; a timing corresponding to a signal proportional to a variation in the motor speed or the motor speed; a timing corresponding to a delayed time with respect to the start/stop of the motor; a timing corresponding to a variation in the powersupply voltage or a signal proportional to a variation in the powersupply voltage; and a timing corresponding to the negative current or a signal proportional to the negative current.
Employing one of these timings enables low power consumption, low costs, high performance, and other advantages to be obtained.
In this second aspect, the regeneration current control means may be operable to switch between a synchronous rectification PWM mode and a one-way PWM mode, the synchronous rectification PWM mode being for driving both of the upper drive means and the lower drive means to perform the PWM operation and the one-way PWM mode being for driving only one of the upper drive means and the lower drive means to perform the PWM operation.
In this case, the motor is controlled using a PWM signal proportional to the torque command signal, and the switching is performed between the synchronous rectification PWM mode and the one-way PWM mode. As such, the above arrangement has an advantage in that the switching is performed for the path through which a regeneration current flows because of the PWM operation, thereby preventing occurrence of negative current.
The third aspect of the present invention provides a motor and an information equipment such as a processing device each using the driver of the first and second aspect of the present invention, thereby implementing low power consumption and solving various problems occurring because of negative current.